The invention relates to a power plant with at least one turbo group and with a recuperator. The invention relates, moreover, to a method for starting a power plant of this type.
A power plant of the type initially mentioned conventionally comprises a turbo group with at least one turbine and with at least one main burner which is arranged upstream of the turbine and, during operation, generates hot gases which act upon the turbine. A generator for current generation may be drive-connected to this turbo group. In normal operation, with the aid of a recuperator which is arranged, on the one hand, in a first flow path leading gas toward the turbo group and, on the other hand, in a second flow path leading gas away from the turbo group, heat is extracted from the gases emerging from the turbo group, in order thereby to preheat the gases delivered to the turbo group. To increase efficiency, an additional burner, by means of which the temperature level of the preheated gases delivered to the turbo group can be additionally increased, may be arranged in the recuperator in the second flow path of the gases emerging from the turbo group.
The power plant can be shut down during times of low current demand, for example at night or weekends, or for maintenance purposes. As a result, in particular, the turbo group and the recuperator cool down to a greater or lesser extent. In this case, as a rule, the recuperator cools down more quickly than the components of the turbo group. So that the power plant or the respective turbo group can develop its full power output as rapidly as possible, it is expedient for the recuperator to be preheated. In a power plant which is designed as a gas storage power plant and the turbo group of which is equipped with an additional turbine arranged upstream of the main burner, thermal stresses in the components of the additional turbine, for example in guide vanes and moving blades, can thereby be reduced. By virtue of the reduction in thermal stresses, the useful life of individual components of the power plant can thus also be increased.
To preheat the recuperator, it is basically possible for the recuperator to be preheated by putting into operation the additional burner arranged in the recuperator. However, this may lead in the recuperator, in particular near the additional burner, locally to hot zones or spots, the temperature of which is above a selfignition temperature of a fuel/oxidizer mixture which is delivered to the main burner for combustion in order to start the turbo group. Hot zones or spots of this kind are a disadvantage when an attempt to ignite the main burner fails, since the combustible fuel/oxidizer mixture then comes into contact with these hot zones or spots and may ignite there in an undesirable way.
The invention is intended to remedy this. The invention, as characterized in the claims, is concerned with the problem of finding for a power plant of the type initially mentioned a way which makes it possible to preheat the recuperator, without at the same time giving rise to the risk of critical local hot spots in the recuperator.
This problem is solved by means of the subjects of the independent claims. Advantageous refinements are presented in the dependent claims.
The present invention is based on the general idea of preheating the recuperator with the aid of an auxiliary burner which is arranged outside the second flow path, that is to say, in particular, outside the recuperator. This measure makes it possible to ensure in a particularly simple way that the critical selfignition temperature of the fuel/oxidizer mixture is not reached at any point in the second flow path and therefore in the recuperator. The invention thus makes it possible, should an attempt to ignite the main burner fail, to reduce or to avoid the risk of an undesirable selfignition of the fuel/oxidizer mixture in the system as a whole.
Since the auxiliary burner used for preheating the recuperator is arranged outside the second flow path, the temperature in the second flow path or in the recuperator cannot at any point be higher than the temperature which the gas generated by the auxiliary burner and fed into the second flow path possesses, this temperature being relatively easily controllable. In particular, in the case of this externally arranged auxiliary burner, it is unimportant whether the critical selfignition temperature is exceeded or not locally in it, since the external auxiliary burner cannot come into contact with the explosive fuel/oxidizer mixture even in the event of a misignition of the main burner. It may even be expedient first, with the aid of the additional burner, to generate hot gases, the temperature of which is above the critical selfignition temperature, appropriate quantities of cold gases being admixed before the feed into the second flow path, in order to lower the temperature of the gas mixture ultimately delivered to the second flow path below the critical selfignition temperature. This admixing of cold gas preferably already takes place within the auxiliary burner, for example by means of a corresponding secondary gas supply.
The power plant proposed according to the invention and the starting method according to the invention are particularly suitable for use in what is known as a xe2x80x9ccompressed-air energy-storage systemxe2x80x9d, CAES system in brief. The basic idea of a CAES system is seen in transferring excess energy generated by permanently operated power stations during the basic-load times into the peak-load times. This is achieved in that, with the aid of the excess energy, air or another gas is pumped under a relatively high pressure into a store, from which the air or the gas can be extracted, as required, for current generation. This means that the energy is kept retrievably in stock in the form of potential energy. Used-up coalmines, limestone quarries or salt mines, for example, serve as stores.
Further important features and advantages of the invention may be gathered from the subclaims, from the drawing and from the accompanying FIGURE description with reference to the drawing.